Flooding packets on a per-virtual-network basis

ABSTRACT

Methods and techniques for flooding packets on a per-virtual-network basis are described. Some embodiments provide a method (e.g., a switch) which determines an internal virtual network identifier based on one or more fields in a packet&#39;s header. Next, the method performs a forwarding lookup operation based on the internal virtual network identifier. If the forwarding lookup operation succeeds, the method can process and forward the packet accordingly. However, if the forwarding lookup operation fails, the method can determine a set of egress ports based on the internal virtual network identifier. Next, for each egress port in the set of egress ports, the method can flood the packet if a virtual network identifier in the packet&#39;s header is associated with the egress port. Flooding packets on a per-virtual-network basis can substantially reduce the amount of resources required to flood the packet when a forwarding lookup operation fails.

RELATED APPLICATION

This application claims priority to U.S. Provisional Application No. 61/352,727, entitled “Per-VPN Flooding,” filed 8 Jun. 2010, the contents of which are incorporated by reference herein.

This application also claims priority to U.S. Provisional Application No. 61/427,050, entitled “Flooding Packets on a Per-Virtual-Network Basis,” filed 23 Dec. 2010, the contents of which are incorporated by reference herein.

BACKGROUND

Technical Field

This disclosure relates to data communication and networking More specifically, this disclosure relates to systems and techniques for flooding packets on a per-virtual-network basis.

Related Art

Computer networks have become critical elements of the information technology infrastructure. The insatiable demand for bandwidth and the ever increasing size and complexity of computer networks has created a need for increasing the bandwidth and improving manageability of computer networks.

The manageability of computer networks can be improved by using network virtualization. In network virtualization, a large and complex network can be arbitrarily carved up into multiple virtual networks to facilitate manageability. In some networks, a switch may flood a packet if a forwarding lookup operation for the packet fails. Unfortunately, flooding a packet in a network can consume a large amount of network resources.

SUMMARY

Some embodiments of the present invention provide systems and techniques for flooding packets on a per-virtual-network basis. During operation, a system (e.g., a switch) can receive a packet. Next, the system can determine an internal virtual network identifier based on one or more fields in a packet and/or a port on which the packet was received. The one or more fields in the packet can include, but is not limited to, a customer VLAN (Virtual Local Area Network) identifier, a service provider VLAN identifier, a source MAC (medium access control) address, a destination MAC address, an ingress RBridge (routing bridge) nickname, an egress RBridge nickname, and/or a Virtual Private Network (VPN) identifier. Packets from different virtual networks may be mapped to the same internal virtual network identifier. The system can then perform a forwarding lookup operation based on the internal virtual network identifier. If the forwarding lookup operation fails, the system can determine a set of egress ports based on the internal virtual network identifier. Next, the system can flood the packet over an egress port in the set of egress ports if a virtual network identifier (e.g., a VPN identifier) in the packet's header is associated with the egress port. In general, the virtual network identifier can include one or more fields in the packet that are used for identifying a virtual network. Note that flooding packets on a per-virtual-network basis can substantially reduce the amount of resources required to flood the packet when a forwarding lookup operation fails. Further, flooding packets on a per-virtual-network basis enables the network to keep traffic from different virtual networks separate. In this disclosure, unless otherwise stated, the phrase “based on” means “based solely or partly on.”

In some embodiments, the system can determine the set of egress ports by first determining a multicast tree based on the virtual network identifier, and then determining the set of egress ports based on the multicast tree.

In some embodiments, the system can provide a copy of the packet to a set of egress ports. Next, each egress port can then use the VPN identifier to determine whether or not to flood the packet over the port. Specifically, each egress port can flood the packet over the port if the port is coupled to a network that includes hosts that are part of the VPN associated with the VPN identifier.

The virtual network identifier can generally refer to one or more fields in a packet that are used for determining which virtual network the packet belongs to. In some embodiments, the packet is a TRILL (Transparent Interconnection of Lots of Links) packet and the virtual network identifier is a VPN identifier. In some embodiments, the packet is a VLAN packet and the virtual network identifier is a VLAN identifier. In some embodiments, the virtual network identifier is a combination of one or more fields in the packet, e.g., the virtual network identifier may be a combination of one or more VLAN identifiers and/or a VPN identifier.

In some embodiments, the system can determine an internal virtual network identifier for a packet based on one of the following field combinations: (1) the MAC source address and the customer VLAN identifier, (2) customer VLAN identifier, (3) customer VLAN identifier and the service provider VLAN identifier, (4) service provider VLAN identifier, (5) customer VLAN identifier and the VPN identifier, and (6) the VPN identifier. In some embodiments, the system can map a TRILL packet to a default internal virtual network identifier, and then selectively flood the TRILL packet on each port associated with the default internal virtual network identifier based on the VPN identifier in the TRILL packet.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a TRILL network in accordance with some embodiments of the present invention.

FIG. 2 illustrates a portion of an Ethernet packet which includes a TRILL header in accordance with some embodiments of the present invention.

FIG. 3 illustrates examples of mappings between packet header information and internal virtual network identifiers in accordance with some embodiments of the present invention.

FIG. 4 illustrates a switch in accordance with some embodiments of the present invention.

FIG. 5 presents a flowchart that illustrates a process for flooding packets on a per-virtual-network basis in accordance with some embodiments of the present invention.

FIG. 6 illustrates a system in accordance with some embodiments of the present invention.

FIG. 7 illustrates how flooding can be performed on a per-virtual-network basis in accordance with some embodiments of the present invention.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

TRILL (Transparent Interconnection of Lots of Links)

TRILL combines the advantages of bridging and routing. Bridges (e.g., devices that perform layer-2 forwarding) can transparently connect multiple links to create a single local area network. Without TRILL, bridges use the spanning tree protocol (STP) which restricts the topology on which traffic is forwarded to a tree to prevent loops. Unfortunately, forwarding the traffic over a tree causes traffic concentration on the links that correspond to the tree edges, leaving other links completely unutilized. Unlike bridges, Internet Protocol (IP) routers (e.g., devices that perform IP forwarding) do not need to create a spanning tree for forwarding traffic. However, routers that forward IP traffic require more configuration than bridges, and moving nodes in an IP network requires changing the IP address of the nodes. Each link in an IP network is associated with an address prefix, and all nodes on that link must have that IP prefix. If a node moves to another link that has a different IP prefix, the node must change its IP address. Unless otherwise stated, the term “IP” refers to both “IPv4” and “IPv6” in this disclosure.

A TRILL network includes “routing bridges” (referred to as RBridges) which route packets, but like bridges, learn layer-2 address locations through receipt of packets. Since packets are routed, packet forwarding is not limited to a spanning tree. Also, since a hop count is included in a TRILL packet, packets do not circulate forever in the network in the presence of loops. Further, since the layer-2 address locations are learned, a TRILL network allows IP nodes to move from one link to another in the network without any restrictions.

FIG. 1 illustrates a TRILL network in accordance with some embodiments of the present invention. TRILL network 100 can be a service provider's network which includes core RBridges 102 and 104 and edge RBridges 106, 108, and 110. RBridges 102, 106, 108, and 110 are coupled to customer devices, whereas RBridge 104 is not. Specifically, port P3 on RBridge 102 can be coupled to a device in customer C3's network at site S1; ports labeled P1 on RBridges 106, 108, and 110 can be coupled to devices in customer C1's networks at sites S2, S3, and S4, respectively; and port P3 on RBridge 110 can be coupled to a device in customer C3's network at site S5. Note that the port numbers in FIG. 1 match the customer numbers, i.e., ports labeled P1 are associated with customer C1, ports labeled P3 are associated with customer C3, etc. This has been done for ease of discourse. In general, any port on any RBridge can potentially be assigned to one or more virtual networks that are associated with one or more customers.

A virtual local area network (VLAN) in a customer's network may span multiple customer sites. For example, VLANs 112 and 114 in customer C3's network include nodes in sites S1 and S5. Similarly, VLANs 116 and 118 in customer C1's network include nodes in sites S2 and S3, and VLAN 120 in customer C1's network includes nodes in sites S3 and S4.

Nodes that belong to the same VLAN, but which are located at different sites, can communicate with each other transparently through TRILL network 100. Specifically, the ingress RBridge can encapsulate a packet (e.g., an Ethernet packet with or without one or more VLAN tags) received from a customer and route the packet within TRILL network 100 using a TRILL header. The egress RBridge can then strip the TRILL header and send the original customer packet on the appropriate port. For example, packet 122 can originate in customer C3's network at site S1, and be received on port P3 of RBridge 102 with a VLAN tag associated with VLAN 112. Next, RBridge 102, which is the ingress RBridge for this packet, can encapsulate packet 122 by adding a TRILL header to obtain packet 124 (the TRILL header is the shaded portion in packet 124). Next, the TRILL header of packet 124 can be used to route packet 124 through TRILL network 100 until packet 124 reaches RBridge 110, which is the egress RBridge for the packet. RBridge 110 can then strip away the TRILL header on packet 124 to obtain the original packet 122, and send packet 122 on port P3 so that the packet can be delivered to the intended destination in VLAN 112 in customer C3's network at site S5. In FIG. 1, the packet that is received at the ingress RBridge and the packet that is sent from the egress RBridge are shown to be the same. However, these packets can be different. For example, if VLAN translation is being performed, then the packet that is received at the ingress RBridge and the packet that is sent from the egress RBridge can have different VLAN tags.

Details of the TRILL packet format and RBridge forwarding can be found in IETF draft “RBridges: Base Protocol Specification,” which is incorporated herein by reference.

Although some examples in this disclosure are presented in the context of a TRILL network that includes RBridges, the present invention is not limited to TRILL networks or RBridges. The terms “frame” or “packet” generally refer to a group of bits. The use of the term “frame” is not intended to limit the present invention to layer-2 networks. Similarly, the use of the term “packet” is not intended to limit the present invention to layer-3 networks. Unless otherwise stated, the terms “frame” or “packet” may be substituted with other terms that refer to a group of bits, such as “cell” or “datagram.”

Network Virtualization

Network virtualization enables a service provider to provision virtual networks (VNs) over a common network infrastructure. To a user on a VN it appears as if the traffic is being carried over a separate network that has been specifically built for the user. However, in reality, the traffic from multiple VNs may be carried over a common network infrastructure.

Network virtualization has many uses. For example, network virtualization can be used to create multiple, logically distinct networks on the same physical network to comply with government regulations. Other uses of network virtualization include, but are not limited to, partitioning network resources between different organizations in a company thereby reducing network costs and simplifying network management.

One approach for addressing the problem that is solved by network virtualization is to duplicate resources (e.g., routers, switches, etc.) in the network so that the resources can be provisioned on a per-customer basis. However, this approach is impractical because it is costly and it is not scalable.

Some embodiments of the present invention implement network virtualization and/or partitioning in the TRILL network by embedding a VPN identifier in a TRILL option field in the TRILL header. Specifically, the ingress RBridge can determine a VPN identifier for each packet it receives from a customer, and embed the VPN identifier in a TRILL option field in the TRILL header. Next, the VPN identifier can be used to support network virtualization and/or partitioning in the TRILL network. Specifically, once the VPN identifier is embedded into the TRILL header, RBridges in the TRILL network can use the VPN identifier to determine how to handle the packet.

In some embodiments, the system can use a service provider VLAN identifier to implement network virtualization and/or partitioning. Specifically, ingress RBridges can add appropriate S-tags to packets received from customers (note that the S-tag based approach may not work for incoming packets that already have an S-tag). Next, the S-tag can be used to implement virtualization and/or partitioning in the network.

Packet Format

FIG. 2 illustrates a portion of an Ethernet packet which includes a TRILL header in accordance with some embodiments of the present invention. The packet shown in FIG. 2 is for illustration purposes only, and is not intended to limit the present invention.

Packet 200 can include one or more of the following fields: outer MAC (medium access control) addresses 202, outer VLAN tag 204, TRILL header field 206, TRILL option field 208, inner MAC addresses 210, and inner VLAN tags 212. Typically, the packet is transmitted from top to bottom, i.e., the bits associated with outer MAC addresses 202 will appear on the transmission medium before the bits associated with outer VLAN tag 204 appear on the transmission medium, and so forth. The contents of these fields and their uses are discussed below.

Outer MAC addresses 202 can include outer destination MAC address 214 and outer source MAC address 216. These MAC addresses and outer VLAN tag 204 typically change at each TRILL hop as the packet traverses the service provider's network. Specifically, at each hop, outer source MAC address 216 is associated with the MAC address of the source node (e.g., RBridge) for that hop, outer destination MAC address 214 is associated with the MAC address of the destination node (e.g., RBridge) for that hop, and outer VLAN tag 204 is associated with the VLAN that includes the source node and the destination node for that hop.

Outer VLAN tag 204 can include Ethernet type field 218 and outer VLAN identifier 220. The value of Ethernet type field 218 can indicate that the next field is a VLAN identifier. VLAN identifier 220 can be used in the service provider's network to create multiple broadcast domains.

TRILL header field 206 can include Ethernet type field 222 and TRILL header 224. The value of Ethernet type field 222 can indicate that the next field is a TRILL header. TRILL header 224 can include information for routing the packet through a TRILL network that is embedded in the service provider's network. Specifically, as shown in FIG. 2, TRILL header 224 can include version field 246 which indicates the TRILL version, reserved field 248 which may be reserved for future use, multicast field 250 which indicates whether this packet is a multicast packet, TRILL option length 252 which indicates the length (in terms of 32-bit words) of any TRILL option field that follows the TRILL header, and hop count 254 which may be decremented at each RBridge as the packet traverses the service provider's network.

TRILL header 224 also includes egress RBridge nickname 256 and ingress RBridge nickname 258. Ingress RBridge nickname 258 corresponds to the ingress RBridge which receives the packet from the customer's network, and, for unicast packets, egress RBridge nickname 256 corresponds to the egress RBridge which sends the packet to the customer's network. For multicast packets, egress RBridge nickname 256 corresponds to the RBridge which is the root of the multicast tree on which the packet is to be forwarded. For example, in FIG. 1, when packet 122 is received at ingress RBridge 102, ingress RBridge 102 can use the header information in packet 122 to determine that packet 122 needs to be routed to egress RBridge 110. Next, ingress RBridge 102 can add TRILL header field 206 to packet 122 to obtain packet 124. Specifically, RBridge 102 can set ingress RBridge nickname 258 in packet 124's TRILL header to RBridge 102's nickname, and set egress RBridge nickname 256 in packet 124's TRILL header to RBridge 110's nickname. RBridge 102 can then forward packet 124 based solely or partly on packet 124's TRILL header.

TRILL option field 208 can include bit-encoded options and one or more options encoded in a TLV (type-length-value) format. Specifically, TRILL option field 208 can include bit-encoded options 260 which are one-bit option flags, and TLV-encoded option 226. For example, a 20-bit VPN identifier can be encoded as a TLV-encoded option. Specifically, the value of type field 262 can indicate that this option specifies a VPN identifier. Length field 264 can indicate the length of the data portion of the TLV-encoded option in octets. In the packet shown in FIG. 2, TLV-encoded option 226 is used for specifying a 20-bit VPN identifier, and length field 264 is set to the value 0x6. The data portion of TLV-encoded option 226 begins immediately after length field 264. Specifically, in the packet shown in FIG. 2, the total length (in octets) of fields 266, 268, and 228 is equal to 0x6 as specified by length field 264. Further, as shown in FIG. 2, the last 20 bits of the data portion in TLV-encoded option 226 can be used for specifying VPN identifier 228.

Note that a 20-bit VPN identifier can be specified using a smaller data portion, e.g., only 0x3 octets instead of 0x6 octets. However, some embodiments use the following non-obvious insight: it may be desirable to align the 20-bit VPN identifier with the word boundary to simplify chip design and/or to improve performance. Thus, in some embodiments, 0x6 octets are used instead of 0x3 octets so that the 20-bit VPN identifier is aligned with a 32-bit word boundary. For example, as shown in FIG. 2, VPN identifier 228 is aligned with the 32-bit word boundary.

Inner MAC addresses 210 can include inner source MAC address 232 and inner destination MAC address 230. Inner MAC addresses 210 can be the MAC addresses that were present in the header of the packet that was received from the customer's network. For example, in FIG. 1, suppose a source node in VLAN 112 in customer C3's network at site S1 sends a packet to a destination node in VLAN 112 in customer C3's network at site S5. In this scenario, inner source MAC address 232 can correspond to the source node at site S1, and inner destination MAC address 230 can correspond to the destination node at site S5.

Inner VLAN tags 212 can include one or more VLAN tags. For example, inner VLAN tags 212 can include an S-tag which includes Ethernet type field 234 and S-VLAN-identifier 236, a C-tag which includes Ethernet type field 238 and C-VLAN-identifier 240, and another tag which includes Ethernet type field 242 and VLAN identifier 244. Each VLAN tag in outer VLAN tag 204 and inner VLAN tags 212 can also include a three-bit Priority Code Point (PCP) field (also referred to as the “priority” or “priority bits” in this disclosure), e.g., PCP 270, and a one-bit CFI field, e.g., CFI 272. When an S-tag is used, the CFI field can carry a drop eligibility indicator (DEI) bit. The values in Ethernet type fields (e.g., 234, 238, and 242) can indicate the type of VLAN tag that follows. For example, Ethernet type field 234 and 238 can indicate a VLAN identifier for an S-tag and a VLAN identifier for the C-tag follow the respective Ethernet type fields. The S-tag and the C-tag can be used by the customer to create a stacked-VLAN architecture, e.g., as defined in the Provider Bridging standard. The S-tag may also be used by the service provider to implement network virtualization and/or partitioning. Packet 200 can also include other tags, each tag having a tag-type field which indicates the type of the tag, and a field that stores contents (e.g., an identifier) related to the tag. For example, packet 200 can include a 32-bit congestion-notification-tag (CN-tag) which includes a 16-bit tag-type field and a 16-bit flow-identifier. The congestion-notification-tag may be used by the customer to manage network congestion.

Note that a packet may or may not include all of the fields shown in FIG. 2. For example, in some embodiments, a packet may not include one or more of inner VLAN tags 212 and/or outer VLAN tag 204. Further, certain combinations of fields may not be allowed in some embodiments. For example, in some embodiments, a packet may include either an S-tag or a TRILL option field, but not both. Additionally, the values of some fields may be related to each other. For example, in some embodiments, S-VLAN-identifier 236 may be copied into the 12 least significant bits of VPNID 228.

VLAN tagging is specified in IEEE (Institute of Electrical and Electronics Engineers) standard IEEE 802.1Q. The earlier versions of the standard, including and up to IEEE 802.1Q-2005 of this standard describes how a single VLAN tag can be added to an Ethernet packet to create multiple broadcast domains within the same local area network (LAN). The term Provider Bridging refers to an amendment of this standard which allows an S-tag (a service VLAN tag is sometimes referred to as a provider tag) to be stacked in a single Ethernet packet. Provider Bridging enables a service provider to carry VLAN traffic from multiple customers on a shared network infrastructure without restricting the VLAN address space available to each customer. Further details on Provider Bridging can be found in the specification for standard IEEE 802.1ad.

In some embodiments, the system can add a TRILL header to a Provider Bridging packet. In these embodiments, the packet received from the customer network may include an S-tag. The service provider's network may then add a TRILL header to the packet. In some embodiments, the system may ensure that the priority bits in the outermost VLAN tag are the same as the priority bits in the S-tag.

Internal Virtual Network Identifier

When a packet is received on an input port, the packet header is processed by the switch to determine the output port on which the packet is to be forwarded. Oftentimes, the forwarding mechanism (e.g., an integrated circuit specifically designed for performing forwarding lookups) is the bottleneck in the data path. Consequently, increasing the processing speed and decreasing the size and complexity of the forwarding mechanism is usually very important.

One approach for supporting network virtualization in an RBridge is to directly use the VPN identifier and/or other fields in the packet header to perform forwarding lookup. Unfortunately, this approach can require the forwarding mechanism to use a large number of bits to perform the forwarding lookups. As a result, it can be very costly to design a switch that performs forwarding using this approach.

Some embodiments of the present invention determine an internal virtual network identifier based on the port on which a packet is received and/or one or more fields (which may include the VPN identifier) in the packet. Next, the packet is forwarded based on the internal virtual network identifier. The length (in terms of bits) of the internal virtual network identifier can be less than the combined length of the one or more fields in the packet's header that are used for determining the internal virtual network identifier. This reduction in length can increase the processing speed of the forwarding mechanism, and decrease the overall size and complexity of the implementation.

There are at least two non-obvious insights that allow us to map the one or more fields in the packet's header to a shorter sized internal virtual network identifier without significantly affecting network virtualization functionality. The first non-obvious insight is that, even though each customer is given the capability to create a large number of virtual networks, it is unlikely that each and every customer will provision a large number of virtual networks. For example, even though each customer may be given the capability to create 4K VLANs, it is unlikely that each and every customer will provision 4K VLANs. Hence, the internal virtual network identifier does not have to be long enough to handle cases in which each customer provisions 4K VLANs. Note that the entire 4K VLAN address space is still available to each customer.

The second non-obvious insight is that multiple virtual networks can be mapped to a single internal virtual network identifier. Note that an RBridge needs to assign a unique internal virtual network identifier for a virtual network if the RBridge needs to forward packets to a customer on a local port. For example, an ingress or egress RBridge may assign a unique internal virtual network identifier for each virtual network whose packets are forwarded to a customer-facing port on the RBridge. However, if the RBridge is not an ingress or egress RBridge for a set of virtual networks, then the RBridge can map the set of virtual networks to a common “pass-through” internal virtual network identifier. For example, the RBridge can map multiple (VLAN identifier, VPN identifier) tuples to the same internal virtual network identifier if the RBridge is not an ingress or egress RBridge for these (VLAN identifier, VPN identifier) tuples.

FIG. 3 illustrates examples of mappings between packet header information and internal virtual network identifiers in accordance with some embodiments of the present invention.

As mentioned above, the port on which a packet is received and/or one or more fields in the packet's header can be mapped to an internal virtual network identifier. The mappings shown in FIG. 3 map a (VLAN identifier, VPN identifier) tuple from a packet's header to an internal virtual network identifier. The mappings shown in FIG. 3 are for illustration purposes only and are not intended to limit the present invention to the forms disclosed.

The mappings illustrated in FIG. 3 may correspond to RBridges 102, 104, 106, 108, and 110 in FIG. 1. The mapping on RBridge 106 may map (VLAN identifier, VPN identifier) tuples 306 and 308 to internal virtual network identifiers IVNID-01 and IVNID-02, respectively. The mapping on RBridge 108 may map tuples 306, 308, and 310 to internal virtual network identifiers IVNID-03, IVNID-04, and IVNID-05, respectively. The mapping on RBridge 110 may map tuples 302, 304, and 310 to internal virtual network identifiers IVNID-06, IVNID-07, and IVNID-08, respectively.

The mapping on RBridge 102 may map tuples 302 and 304 to internal virtual network identifiers IVNID-09 and IVNID-10, respectively. If the traffic associated with tuples 306, 308, and 310 passes through RBridge 102, these tuples may be mapped to a common internal virtual network identifier, namely, IVNID-11. If all traffic passes through RBridge 104, the RBridge may map all tuples to a common internal virtual network identifier, namely, IVNID-12.

In some embodiments, the scope of internal virtual network identifiers does not extend beyond an RBridge. Hence, different RBridges may map the same tuple to different internal virtual network identifiers. For example, the tuple 306 is mapped to internal virtual network identifiers IVNID-01, IVNID-03, IVNID-11, and IVNID-12 on RBridges 106, 108, 102, and 104, respectively.

When RBridge 106 receives a packet on port P1 whose header information includes tuple 306, it can use the mapping shown in FIG. 3 to determine the associated internal virtual network identifier, namely, IVNID-01. Next, RBridge 106 can forward the packet based on IVNID-01. Specifically, RBridge 106 can perform a forwarding lookup using IVNID-01 as the key. The result of the lookup operation may indicate that a TRILL header is to be added to the packet to obtain a TRILL packet, and that the resulting TRILL packet is to be forwarded to RBridge 102. At RBridge 102, the TRILL packet may be forwarded to RBridge 108 based on the TRILL header.

Note that RBridge 102 may determine an internal virtual network identifier (e.g., IVNID-11) based on the header information. However, since the packet has a TRILL header, the internal virtual network identifier may be ignored by RBridge 102 for purposes of forwarding the packet (assuming that the packet is not destined for VLANs 112 or 114).

When the packet is received at RBridge 108, an internal virtual network identifier (e.g., IVNID-03) may be determined based on the header information. Next, the internal network identifier may be used to perform a forwarding lookup. The result of the lookup operation may indicate that the packet is to be forwarded on port P1 to VLAN 116. Accordingly, RBridge 108 may forward the packet on port P1 to VLAN 116.

Per-Virtual-Network Flooding

If a forwarding lookup operation fails, a switch may flood the packet to ensure that the packet reaches its intended destination. Unfortunately, flooding can consume a large amount of network resources. Therefore, it is generally desirable to limit the extent of flooding if possible.

In an IVNID based approach, packets from multiple virtual networks (e.g., VPNs or VLANs) may be mapped to the same IVNID value. For example, in FIG. 3, (VLAN identifier, VPN identifier) tuples 306, 308, and 310 are mapped to the same IVNID value on RBridge 102. In one approach, if a forwarding lookup operation for a packet fails, the switch may flood the packet to at least those virtual networks that map to the IVNID for the packet. For example, if a forwarding lookup operation on Rbridge 102 fails for a packet associated with IVNID-11, Rbridge 102 may flood the packet at least on all ports that are associated with tuples 306, 308, and/or 310.

Flooding a packet on more virtual networks than necessary can waste networking resources. Therefore, in some embodiments of the present invention, flooding is performed on a per-virtual-network basis. Specifically, in some embodiments, filtering at the ports is performed based on the VPN identifier, and if the packet does not include a VPN identifier field, a VPN identifier can be determine based on other fields in the packet (e.g., the VPN identifier can be determined based on the S-VLAN identifier). For example, RBridge 102 can determine a set of egress ports based on an IVNID. Next, RBridge 102 can provide a copy of the packet to the set of egress ports. Each egress port can then flood the packet only if the virtual network identifier in the packet (e.g, a VPN identifier in the TRILL header or a VPN identifier that is determined based on other fields in the packet) is associated with the egress port. In other words, once the packet has been provided to the set of egress ports based on the IVNID, the egress ports can then filter packets based on a virtual network identifier field in the packets. For example, as shown in FIG. 3, all packets are mapped to IVNID-12 on RBridge 104. In this case, if the forwarding lookup fails, the packet can be provided to all egress ports on RBridge 104. Each egress port can then flood the packet depending on whether or not the egress port is associated with the virtual network identifier in the packet.

FIG. 4 illustrates a switch in accordance with some embodiments of the present invention.

Switch 400 can include a plurality of mechanisms which may communicate with one another via a communication channel, e.g., a bus. Switch 400 may be realized using one or more integrated circuits. In some embodiments, switch 400 is an RBridge (e.g., RBridge 102) which includes forwarding lookup mechanism 402, determining mechanism 404, and flooding mechanism 406. In some embodiments, these mechanisms may be part of an application-specific integrated circuit.

Forwarding lookup mechanism 402 may be configured to perform a forwarding lookup operation based on one or more fields in a packet's header. The one or more fields in the packet's header can include, but are not limited to, a customer VLAN identifier, a service provider VLAN identifier, a source MAC address, a destination MAC address, an ingress RBridge nickname, and an egress RBridge nickname. In some embodiments, forwarding lookup mechanism 402 may be configured to perform a look up using a content-addressable memory.

Switch 400 may determine an internal virtual network identifier for a packet (e.g., Ethernet packet) based on the port on which the packet is received and/or one or more fields in the packet's header. The switch and/or port configuration can dictate which fields are used to determine the internal virtual network identifier. For example, one port of a switch may be configured to map all packets to a particular internal virtual network identifier. Another port of the switch may be configured to map a set of C-VLAN-identifiers to a corresponding set of internal virtual network identifiers, and assign a default internal virtual network identifier to a packet if the C-VLAN-identifier is not in the set of C-VLAN-identifiers.

If the forwarding lookup operation is successful, switch 400 may forward the packet based on the result of the forwarding lookup operation and the internal virtual network identifier. The switch may include a table (e.g., an array in memory) which is indexed using the internal virtual network identifier. Each record in the table (e.g., an array element) can include information that is used for forwarding the packet. For example, the record may include instructions and/or information for modifying one or more fields in the header (e.g., the record may indicate that VLAN translation is to be performed and specify the new VLAN identifier). Additionally, the record may indicate the header fields that need to be added to the packet (e.g., a TRILL header). Once the packet is provided to the egress ports, the system can determine the encapsulation for the packet. Specifically, at the egress port the system can determine whether to send the packet through the egress port with a C-tag, an S-tag, a TRILL header, and/or a TRILL option field that contains a VPN identifier. The system can also perform translation operations, such as translating a C-tag, an S-tag, and/or a VPN identifier.

However, if the forwarding lookup operation fails, determining mechanism 404 may determine a set of egress ports based on a virtual network identifier in the packet's header. For example, the system can determine the set of egress ports based on a VLAN identifier in a VLAN tag or a VPN identifier in a TRILL option field, or a combination thereof.

Flooding mechanism 406 may be configured to flood the packet over the set of egress ports. Since flooding is performed on a set of egress ports that were determined based on a virtual network identifier in the packet's header, the flooding is more efficient than approaches that flood the packet over all ports regardless of whether or not a particular node in the network belongs to the virtual network associated with the packet.

In some embodiments, the packet is flooded by forwarding the packet over a multicast tree which may be determined based on the virtual network identifier in the packet's header. Specifically, switch 400 can create a TRILL multicast packet whose header includes a multicast tree identifier. Next, switch 400 can forward the TRILL multicast packet over the set of egress ports associated with the multicast tree identifier. In some embodiments, the multicast tree identifier is a nickname of an RBridge that is the root of the multicast tree.

Note that FIG. 4 is for illustration purposes only, and is not intended to limit the present invention to the forms disclosed. In some embodiments, switch 400 may not be an RBridge, and/or may include fewer or more mechanisms than those shown in FIG. 4.

In some embodiments, determining mechanism 404 may determine a set of egress ports based on an IVNID associated with the packet, and/or one or more fields in the packet's header. Next, flooding mechanism 406 can provide a copy of the packet to each egress port in the set of egress ports. Flooding mechanism 406 can then flood a copy of the packet over an egress port only if a virtual network identifier in the packet is associated with the egress port. For example, if an egress port is not coupled to a customer network that is associated with the virtual network identifier, then the egress port may filter out the packet.

FIG. 5 presents a flowchart that illustrates a process for flooding packets on a per-virtual-network basis in accordance with some embodiments of the present invention.

The process can be performed by a switch, e.g., RBridge 102. Upon receiving a packet, the switch can determine an internal virtual network identifier based on one or more fields in a packet and/or a port on which the packet was received (operation 502). Next, the system can perform a forwarding lookup operation based on the internal virtual network identifier (operation 504).

If the forwarding lookup operation succeeds, the switch can process and forward the packet accordingly (operation 506). However, if the forwarding lookup operation fails, the switch can determine a set of egress ports based on the internal virtual network identifier (operation 508). Next, the switch can provide a copy of the packet to each egress port in the set of egress ports (operation 510). The system can then flood a packet on an egress port if a virtual network identifier in the header of the packet is associated with the egress port (operation 512). For example, the system can flood a packet on an egress port if a VPN identifier in the packet indicates that the egress port is coupled to a virtual network associated with the VPN identifier.

FIG. 6 illustrates a system in accordance with some embodiments of the present invention.

System 600 can include processor 602 (e.g., a network processor) and memory 604. Processor 602 may be capable of accessing and executing instructions stored in memory 604. For example, processor 602 and memory 604 may be coupled by a bus. Memory 604 may store instructions that when executed by processor 602 cause system 600 to perform the process illustrated in FIG. 5. Specifically, in some embodiments, memory 604 may store instructions for performing a forwarding lookup operation based on one or more fields in a packet's header, determining a set of egress ports based on a virtual network identifier in the packet's header if the lookup operation fails, and flooding the packet over the set of egress ports.

FIG. 7 illustrates how flooding can be performed on a per-virtual-network basis in accordance with some embodiments of the present invention.

RBridges 702-716 can be in a TRILL network. RBridges 702, 708, and 716 can be coupled to customer networks that are part of the same virtual network. For example, RBridges 702, 704, 708, and 716 may be coupled to VLAN 718 at different customer sites. Suppose RBridge 710 receives a packet from RBridge 704 that includes a VLAN identifier associated with VLAN 718. If a forwarding lookup operation for the packet fails at RBridge 710, RBridge 710 can encapsulate the packet in a TRILL multicast packet, and forward the TRILL multicast packet over the multicast tree, as shown in FIG. 7 using dotted lines.

Note that the TRILL multicast tree is rooted at RBridge 710. In some embodiments, the TRILL multicast packet header can include a field (e.g., multicast field 250 in FIG. 2) which indicates that the packet is a multicast packet. Further, the TRILL multicast packet header can include a multicast tree identifier as the egress RBridge nickname which identifies the multicast tree over which the TRILL multicast packet is to be forwarded. For example, the egress RBridge 256 field in FIG. 2 can be used as the multicast tree identifier by setting it to be the nickname of an RBridge which is the root of the multicast tree.

The data structures and code described in this disclosure can be partially or fully stored on a non-transitory computer-readable storage medium and/or a hardware module and/or a hardware apparatus. A computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other non-transitory media, now known or later developed, that are capable of storing code and/or data. Hardware modules or apparatuses described in this disclosure include, but are not limited to, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), dedicated or shared processors, and/or other hardware modules or apparatuses now known or later developed. Specifically, the methods and/or processes may be described in a hardware description language (HDL) which may be compiled to synthesize register transfer logic (RTL) circuitry which can perform the methods and/or processes.

The methods and processes described in this disclosure can be partially or fully embodied as code and/or data stored in a computer-readable storage medium or device, so that when a computer system reads and/or executes the code and/or data, the computer system performs the associated methods and processes. The methods and processes can also be partially or fully embodied in hardware modules or apparatuses, so that when the hardware modules or apparatuses are activated, they perform the associated methods and processes. Further, the methods and processes can be embodied using a combination of code, data, and hardware modules or apparatuses.

The foregoing descriptions of embodiments of the present invention have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners having ordinary skill in the art. Additionally, the above disclosure is not intended to limit the present invention. The scope of the present invention is defined by the appended claims. 

What is claimed is:
 1. A switch, comprising: one or more ports; lookup circuitry configured to determine an internal virtual network identifier for a packet based on an entry in a data structure in a local storage device, wherein the entry maps a virtual local area network (VLAN) identifier and a Virtual Private Network (VPN) identifier associated with the packet to the internal virtual network identifier; determining circuitry configured to, in response to determining that the packet needs flooding, determine a set of egress ports from the one or more ports for flooding the packet based on the internal virtual network identifier; and flooding circuitry configured to: determine whether to filter the packet for flooding at a first port in the set of egress ports based on whether the first port is associated with the VPN identifier; in response to determining not to filter the packet, associate the packet with the first port as an output port.
 2. The switch of claim 1, wherein the determining circuitry is further configured to determine the internal virtual network identifier based on one or more of: one or more fields in a header of the packet; and a port on which the packet has been received.
 3. The switch of claim 1, wherein the VLAN identifier in the entry is a customer VLAN identifier.
 4. The switch of claim 1, wherein the VLAN identifier in the entry is a service provider VLAN identifier.
 5. The switch of claim 1, wherein the flooding circuitry is further configured to filter the packet for flooding at a second port in the set of egress ports in response to the second port not being associated with the VPN identifier.
 6. The switch of claim 5, wherein the flooding circuitry, in response to filtering the packet for flooding at the second port, is further configured to preclude the second port from being an output port for the packet.
 7. The switch of claim 1, wherein the entry further maps a media access control (MAC) address of the packet to the internal virtual network identifier.
 8. The switch of claim 1, wherein the packet is a packet in a routed network, and wherein the VPN identifier is in a header of the packet associated with the routed network.
 9. The switch of claim 1, wherein packets from a plurality of virtual networks are mapped to the internal virtual network identifier; and wherein the determining circuitry is further configured to determine a set of egress ports for the packets from the plurality of virtual networks based on the internal virtual network identifier.
 10. A system, comprising: a processor; and a memory storing instructions that when executed by the processor cause the system to perform a method, the method comprising: determining an internal virtual network identifier for a packet based on an entry in a data structure in a local storage device, wherein the entry maps a virtual local area network (VLAN) identifier and a Virtual Private Network (VPN) identifier associated with the packet to the internal virtual network identifier; in response to determining that the packet needs flooding, determining a set of egress ports for flooding the packet based on the internal virtual network; determining whether to filter the packet for flooding at a first port in the set of egress ports based on whether the first port is associated with the VPN identifier; and in response to determining not to filter the packet, associating the packet with the first port as an output port.
 11. The system of claim 10, wherein the method further comprises determining the internal virtual network identifier based on one or more of: one or more fields in a header of the packet; and a port on which the packet has been received.
 12. The system of claim 10, wherein the VLAN identifier in the entry is a customer VLAN identifier.
 13. The system of claim 10, wherein the VLAN identifier in the entry is a service provider VLAN identifier.
 14. The system of claim 10, wherein the method further comprises filtering the packet for flooding at a second port in the set of egress ports in response to the second port not being associated with the VPN identifier.
 15. The system of claim 14, wherein the method further comprises, in response to filtering the packet for flooding at the second port, precluding the second port from being an output port for the packet.
 16. The system of claim 10, wherein the entry further maps a media access control (MAC) address of the packet to the internal virtual network identifier.
 17. The system of claim 10, wherein the packet is forwardable in a routed network, and wherein the VPN identifier is in a header of the packet associated with the routed network.
 18. The system of claim 10, wherein packets from a plurality of virtual networks are mapped to the internal virtual network identifier; and wherein the method further comprises determining a set of egress ports for the packets from the plurality of virtual networks based on the internal virtual network identifier.
 19. A method, comprising: determining, by a computing system, an internal virtual network identifier for a packet based on an entry in a data structure in a local storage device, wherein the entry maps a virtual local area network (VLAN) identifier and a Virtual Private Network (VPN) identifier associated with the packet to the internal virtual network identifier; in response to determining that the packet needs flooding, determining a set of egress ports for flooding the packet based on the internal virtual network identifier; determining whether to filter the packet for flooding at a first port in the set of egress ports based on whether the first port is associated with the VPN identifier; and in response to determining not to filter the packet, associating the packet with the first port as an output port.
 20. The method of claim 19, further comprising determining the internal virtual network identifier based on one or more of: one or more fields in a header of the packet; and a port on which the packet has been received.
 21. The method of claim 20, wherein the VLAN identifier in the entry is one or more of: a customer VLAN identifier; and a service provider VLAN identifier.
 22. The method of claim 19, wherein the packet is forwardable in a routed network, and wherein the VPN identifier is in a header of the packet associated with the routed network.
 23. The method of claim 19, wherein packets from a plurality of virtual networks are mapped to the internal virtual network identifier.
 24. The method of claim 19, further comprising: filtering the packet for flooding at a second port in the set of egress ports in response to the second port not being associated with the VPN identifier; and in response to filtering the packet for flooding at the second port, precluding the second port from being an output port for the packet. 